Video systems, such as medical diagnostic imaging systems (CT, MRI, PET, US) generate high frequency signals which may have frequency components ranging from 30 HZ (Hertz) to 150 Mhz (Megahertz). It is necessary in many instances, to isolate such signals from other devices which use these signals, for purposes of personnel (patient) safety. Recent regulatory requirements have placed a demand on achieving such isolation in a form that is backward compatible with existing systems such as printers and workstations.
Conventional opto-isolators are limited in their frequency response and cannot be used. Digitization of the high frequency video signal and then isolating the digital portion optically, is expensive, especially if the digitized signal has to reconverted to an analog signal for purposes of backward compatibility. Direct transformer isolation of these signals is not feasible because the bandwidth requirements dictated by such signals would require both a high and a low frequency response from the transformer.
U.S. Pat. No. 5,574,749, issued Nov. 12, 1996, inventors Nelson et al., discloses a technique for isolating data terminal equipment from a transmission line. The technique uses balanced mixers and isolating capacitors to handle 10 Mhz signals. There is no disclosure that the technique can be used to isolate high frequency signals having a frequency of several hundred Mhz or that high frequency transformers can be used instead of the lower frequency capacitors.